1. Field of the Invention
The present invention refers to an apparatus for fixation to human bone, and in particular to a human spine for use during spinal surgery.
More specifically it refers to such an instrument which includes at least two units which may be secured to spinal vertebrae by means of so called bone screws and which are connected to each other by connecting means, the connecting means being capable of varying their length such as screw spindles. One of said units is provided to be secured to the sacrum portion of the spine.
2. Description of the Related Art
A problem frequently encountered during surgery in the sacrum region involves the structure of the bone material to which the instrument is to be secured. The bone structure at the sacrum is spongy and often osteoporotic in nature. This is particularly true for elderly persons.
For this and other reasons, securing an instrument to the sacrum is effected by means of one and sometimes two bone screws. The type of bone screws which hitherto have been suggested have not resulted in the strong anchoring which is a necessity for the intended operation.
Thus the object of an invention is to overcome this disadvantage and to provide an instrument which rapidly and easily may be secured in the most reliable manner.
A further object is to accomplish a hinge connection between the unit secured to the sacrum and one or several vertebrae situated above the sacrum, without being hindered by the angular condition of this portion of the spine, thereby making it possible to lock a setting even after having screwed in the bone screws.
A third object is to provide an instrument which makes it possible for the surgeon to accomplish all the settings and lockings from one direction and preferably by means of one single tool.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages may be realized by means of the instrumentaties and combinations particularly pointed out in the appended claims.